Hach DR2400 - Page 172

Chlorine, Free
Chlorine, Free
Page 2 of 4
ChlorineFre_MP_High_DPD_Eng_2400.fm
Interferences
5. Remove the cell from
the adapter and add the
contents of one DPD Free
Chlorine powder pillow
to the sample. Cap and
shake the cell about 20
seconds to dissolve.
6. Place the prepared
sample into the adapter.
7. Touch Read.
Results will appear in
mg/L Cl
2
.
Interfering Substance Interference Levels and Treatments
Acidity
Greater than 150 mg/L CaCO
3
. May not develop full color or color may fade instantly. Neutralize
to pH 6–7 with1 N Sodium Hydroxide (Cat. No. 1045-32). Determine amount to be added on
separate sample aliquot, then add the same amount to the sample being tested. Correct for
volume addition (see Section 3.1.3 Correcting for Volume Additions).
Alkalinity
Greater than 250 mg/L CaCO
3
. May not develop full color or color may fade instantly. Neutralize
to pH 6–7 with 1 N Sulfuric Acid (Cat. No. 1270-32). Determine amount to be added on separate
sample aliquot, then add the same amount to the sample being tested. Correct for volume addition
(see Section 3.1.3 Correcting for Volume Additions).
Bromine, Br
2
Interferes at all levels
Chlorine Dioxide, ClO
2
Interferes at all levels
Chloramines, organic May interfere
Iodine, I
2
Interferes at all levels
Manganese, oxidized (Mn
4+
,
Mn
7+
) or Chromium, oxidized
(Cr
6+
)
1. Adjust sample pH to 6–7 with 1.000 N Sulfuric Acid (Cat. No. 1270-32).
2. Add 2 drops Potassium Iodide (30 g/L) (Cat. No. 343-32) to a 5-mL sample.
3. Mix and wait 1 minute.
4. Add 2 drops Sodium Arsenite* (5 g/L) (Cat. No. 1047-32) and mix.
5. Analyze the treated sample as described in the procedure above.
6. Subtract the result of this test from the original analysis to obtain the correct concentration.
Monochloramine (NH
2
Cl)
For conventional free chlorine disinfection (beyond the “breakpoint”), typical monochloramine
concentrations are very low. If monochloramine is present in the sample, its interference in the
free chlorine test is dependent on sample temperature, relative concentration of
monochloramine to free chlorine, and the time required to perform the analysis.
Typical interference levels of NH
2
Cl (1 minute test time, interference as mg/L Cl
2
):
Read
NH
2
Cl Level
Sample Temperature ° C (° F)
5 (41) 10 (50) 20 (68) 30 (86)
1.2 mg/L +0.15 0.19 0.30 0.29
2.5 mg/L +0.35 0.38 0.55 0.61
3.5 mg/L +0.38 0.56 0.69 0.73
5.0 mg/L +0.68 0.75 0.93 1.05